Method and apparatus for transmitting acknowledgements in response to received frames

ABSTRACT

A method and apparatus for transmitting acknowledgements in response to data packets in wireless communication are disclosed. A recipient may receive a plurality of data packets from a plurality of stations and transmit acknowledgements for the data packets to the originating stations in a single transmission. The acknowledgements may be transmitted using multi-user multiple-input multiple-output (MU-MIMO). Alternatively, the acknowledgements may be aggregated and transmitted in the single transmission. A short acknowledgement (ACK) frame may be sent in response to a received frame. The short ACK frame may include an ACK sequence corresponding to a sequence identity (ID) included in the received frame. The short ACK frame may include a short training field (STF) and the ACK sequence. The short ACK frame may be transmitted with a short ACK indication. The short ACK frame may be sent in response to an indication included in the received frame.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application Nos.61/646,040 filed May 11, 2012, 61/669,390 filed Jul. 9, 2012, 61/699,531filed Sep. 11, 2012, and 61/724,466 filed Nov. 9, 2012, the contents ofwhich are hereby incorporated by reference herein.

BACKGROUND

A wireless local area network (WLAN) in the infrastructure basic serviceset (BSS) mode has an access point (AP) for the BSS, and one or morestations (STAs) associated with the AP. The AP typically has access orinterface to a distribution system (DS) or another type of wired orwireless network that carries traffic in and out of the BSS. Traffic toSTAs that originates from outside the BSS arrives through the AP and isdelivered to the STAs. Traffic originating from STAs to destinationsoutside the BSS is sent to the AP to be delivered to the respectivedestinations. Traffic between STAs within the BSS may also be sentthrough the AP where the source STA sends traffic to the AP and the APdelivers the traffic to the destination STA. Such traffic between STAswithin a BSS is really peer-to-peer traffic. The peer-to-peer trafficmay be sent directly between the source and destination STAs with adirect link setup (DLS) using an IEEE 802.11e DLS or an IEEE 802.11ztunneled DLS (TDLS). A WLAN in an independent BSS mode (IBSS) has no APand STAs communicate directly with each other.

In the current IEEE 802.11 infrastructure mode of operation, the APtransmits a beacon on a channel called primary channel. The primarychannel is 20 MHz wide and is the operating channel of the BSS. Thischannel is also used by the STAs to establish a connection with the AP.The channel access mechanism in an 802.11 system is carrier sensemultiple access with collision avoidance (CSMA/CA). In this mode ofoperation, every STA, including the AP, will sense the primary channeland if the channel is detected to be busy, the STA and the AP backs off.Hence one STA (including AP) can transmit at any given time in a givenBSS.

In IEEE 802.11n, high throughput (HT) STAs may also use 40 MHz widechannel for communication. This is achieved by combining the primary 20MHz channel with another adjacent 20 MHz channel to form a 40 MHz widechannel.

In IEEE 802.11ac, very high throughput (VHT) STAs can support 40 MHz, 80MHz and 160 MHz wide channels. While 40 MHz and 80 MHz channels areformed by combining contiguous 20 MHz channels similar to IEEE 802.11n,160 MHz channel may be formed either by combining 8 contiguous 20 MHzchannels or two non-contiguous 80 MHz channels (80+80 configuration).

The channel operating bandwidth may be reduced for sub 1 GHz modes ofoperation, which is supported in IEEE 802.11af and IEEE 802.11ah.802.11af supports 2 MHz, 4 MHz, and 8 MHz bandwidths for operation in TVwhite space (TVWS). 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16MHz bandwidths for operation in non-TVWS. Some STAs in 802.11ah areconsidered to be sensors with limited capabilities, and may support a 1MHz transmission mode.

SUMMARY

A method and apparatus for transmitting acknowledgements in response todata packets in wireless communication are disclosed. A recipient mayreceive a plurality of data packets from a plurality of stations andtransmit acknowledgements for the data packets to the originatingstations in a single transmission. The acknowledgements may betransmitted using multi-user multiple-input multiple-output (MU-MIMO).The acknowledgements may be delayed in time after receiving the datapackets. The acknowledgements may be transmitted based on an agreedschedule, solicited by the stations, or transmitted without solicitationonce a predetermined number of data packets are received.

Alternatively, the acknowledgements may be aggregated and transmitted inthe single transmission. The acknowledgements may be aggregated in an amedium access control (MAC) service data unit domain, in a MAC protocoldata unit domain, or in a physical layer convergence protocol (PLCP)protocol data unit (PPDU) domain.

A short acknowledgement (ACK) frame may be sent in response to areceived frame. The short ACK frame may include an ACK sequencecorresponding to a sequence ID included in the received frame. The shortACK frame may include a short training field (STF) and the ACK sequence.The short ACK frame may be transmitted with a short ACK indication. Theshort ACK frame may be sent in response to an indication included in thereceived frame.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2 shows a conventional acknowledgement (ACK) frame;

FIG. 3 shows an example message exchange sequence of a data frame and ashort ACK frame;

FIG. 4 shows an example physical layer convergence protocol (PLCP)protocol data unit (PPDU) data frame format;

FIG. 5 shows a normal PPDU and an example short ACK frame with a shortACK indication;

FIG. 6 shows a normal PPDU and an example short ACK frame with anextended short training field (STF);

FIG. 7 shows a conventional medium access control (MAC) frame format;

FIG. 8 shows an example of PPDU frame structure for a MU-MIMO block ACK;

FIG. 9 shows an example message exchange sequence for delayed MU-MIMOblock ACK;

FIG. 10 shows a block ACK request (BAR) frame format;

FIG. 11 shows an example PPDU structure for an aggregated multi-user ACK(A-MU-ACK) frame;

FIGS. 12 and 13 show examples of the ACK or block ACK (BA) MAC protocoldata units (MPDUs) aggregated into the multi-user ACK frame coded with aseparate modulation and coding scheme (MCS);

FIG. 14 shows an example of aggregated multi-user ACK with a separatelong training field (LTF) for each user for implementing various MIMOschemes for the users;

FIG. 15 shows an example of single user piggyback ACK;

FIG. 16 shows an example of single user piggyback ACK aggregated in anMSDU level;

FIG. 17 shows an example of piggyback ACK in an MPDU level;

FIG. 18 shows an example of piggyback ACK in a PPDU level;

FIG. 19 shows an example of multi user piggyback ACK;

FIG. 20 shows a conventional ADDBA Request frame action field format;

FIG. 21 shows a conventional ADDBA Response frame action field format;

FIG. 22 shows a conventional DELBA frame;

FIG. 23 shows an example of ACK fields in the delayed multi-user ACKframe for a pre-arranged group of STAs;

FIG. 24 shows an example of ACK fields in the delayed multi-user ACKframe for ad hoc group of STAs;

FIG. 25 shows a conventional short ACK frame format;

FIG. 26 shows an example of short ACK response;

FIGS. 27 and 28 show example procedures of a speed frame exchange fordownlink and uplink data, respectively;

FIG. 29 shows an example of speed frame exchange using a short ACK frame(or short BA frame) for downlink data;

FIG. 30 shows an example of speed frame exchange using a short ACK (orshort BA) frame for uplink data; and

FIG. 31 shows an example of speed frame exchange using a short PS-Pollframe and a short ACK (or short BA) frame.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the other networks 112. By way of example, the base stations 114a, 114 b may be a base transceiver station (BTS), a Node-B, an eNode B,a Home Node B, a Home eNode B, a site controller, an access point (AP),a wireless router, and the like. While the base stations 114 a, 114 bare each depicted as a single element, it will be appreciated that thebase stations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple-output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 106.

The RAN 104 may include eNode-Bs 140 a, 140 b, 140 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 140 a, 140 b, 140c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 140 a, 140 b, 140 c may implement MIMO technology. Thus,the eNode-B 140 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 140 a, 140 b, 140 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1C, theeNode-Bs 140 a, 140 b, 140 c may communicate with one another over an X2interface.

The core network 106 shown in FIG. 1C may include a mobility managemententity gateway (MME) 142, a serving gateway 144, and a packet datanetwork (PDN) gateway 146. While each of the foregoing elements aredepicted as part of the core network 106, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MME 142 may be connected to each of the eNode-Bs 140 a, 140 b, 140 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 142 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 142 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 144 may be connected to each of the eNode Bs 140 a,140 b, 140 c in the RAN 104 via the S1 interface. The serving gateway144 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 144 may also perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 144 may also be connected to the PDN gateway 146,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The core network 106 may facilitate communications with other networks.For example, the core network 106 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 106 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 106 and the PSTN 108. In addition, the corenetwork 106 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

Other network 112 may further be connected to an IEEE 802.11 basedwireless local area network (WLAN) 160. The WLAN 160 may include anaccess router 165. The access router may contain gateway functionality.The access router 165 may be in communication with a plurality of accesspoints (APs) 170 a, 170 b. The communication between access router 165and APs 170 a, 170 b may be via wired Ethernet (IEEE 802.3 standards),or any type of wireless communication protocol. AP 170 a is in wirelesscommunication over an air interface with WTRU 102 d.

Hereafter, the terminologies “short frame” and “null data packet” (NDP)will be used interchangeably. A short frame (such as short ACK, shortblock ACK, short clear-to-send (CTS), short probe request, etc.) is aphysical layer convergence protocol (PLCP) protocol data unit (PPDU)that carries no data field. Hereafter, the term “STA” (e.g., WTRU) mayinclude a non-AP station or an AP station. The embodiments disclosedherein may be implemented by either a non-AP STA or an AP station (anAP). Embodiments disclosed hereafter may be applied to any IEEE 802.11systems and any other wireless communication systems.

Wireless transmissions can be erroneous even though protectionmechanisms such as channel coding, and interleaving, are utilized toprotect the transmission. Therefore, mechanisms for acknowledgement ofcorrect packet reception have been introduced in WLAN systems. TheSTA/AP which successfully receives a data frame addressed to itselfsends a positive acknowledgement. If a STA/AP transmitting a frame doesnot receive an ACK within a prescribed amount of time, it may assumethat the data frame was not received correctly and retransmit it. Notall data frames can be acknowledged in this way. The 802.11 standardalso supports “no ACK” when the originator indicates that noacknowledgement is expected explicitly from the recipient of the dataframe.

A block ACK was introduced in the 802.11e amendment. A block ACKimproves the system efficiency by allowing the recipient of multipleframes to transmit a single block ACK to acknowledge a block of dataframes. The block ACK may be an immediate block ACK or a delayed blockACK.

FIG. 2 shows a conventional ACK frame 200. A conventional ACK frame 200has a PLCP preamble, which includes a short training field (STF) 202 anda long training field (LTF) 204, a signal (SIG) field 206, and an ACKbody frame 208. The ACK body frame 208 has a 2-byte frame control field210, a 2-byte duration field 212, a 6-byte receiver address (RA) field214, and a 4-byte frame check sequence (FCS) 216. Information carried bythe frame control field 210 indicates that this is an ACK frame. The RAfield 214 indicates the originator of the data exchange session.

A short ACK frame may be used to acknowledge a data frame (or any otherframe) from an originator. FIG. 3 shows an example message exchangesequence of a data frame and a short ACK frame. FIG. 3 also shows anexample PPDU frame structure of the short ACK frame in accordance withone embodiment. An originator transmits a data frame 310 to a recipient,and the recipient decodes the data frame 310 and transmits a short ACKframe 320 to the originator to indicate either successful orunsuccessful decoding of the data frame. In the data frame 310, theoriginator may indicate that the expected ACK transmission will be ashort ACK. The originator may explicitly or implicitly identify an ACKsequence ID in the data frame 310. The recipient then includes acorresponding ACK sequence in the ACK sequence field 324 of the shortACK frame 320.

The short ACK frame 320 includes an STF 322 and an ACK sequence field324. The STF 322 may be utilized for automatic gain control (AGC) andcoarse time frequency offset estimation. The short ACK frame 320 may bedistinguished from other frames by the STF 322.

The ACK sequence which corresponds to the ACK sequence ID indicated bythe data frame 310 indicates the corresponding data frame 310. The ACKsequence may be modulated either in frequency domain or in time domain.For example, a set of pre-defined sequences with the constant amplitudezero auto correlation (CAZAC) property may be used as the ACK sequence.For example, general chirp like (GCL) sequences may be used. TheZadoff-Chu (ZC) sequence is a special case of the GCL sequence. Eachsequence has a sequence ID. The originator implicitly or explicitlyassigns this sequence ID in the transmitted data frame 310. Therecipient includes the corresponding sequence in the short ACK frame320. The short ACK frame 320 may be utilized for simultaneous multipleuser access since orthogonal sequences are chosen.

The originator demodulates a received short ACK frame by correlatingwith the assigned ACK sequence in either frequency domain or timedomain. Once the originator demodulates the short ACK correctly, theoriginator knows that this is an acknowledgment for the previouslytransmitted data packet. False detection might be possible. However, theprobability of false detection may be reduced by increasing the numberof ACK sequences.

Unintended STAs may set their network allocation vector (NAV) when theydemodulate the data packet 310 transmitted from the originator. Theduration field carried by the data packet 310 may be set considering thefact that the following ACK will be a short ACK. If the unintended STAsfail to demodulate the data packet 310 but detects the short ACK STFfield, the unintended STAs identify this is a short ACK frame and maydefer accessing the medium accordingly.

The extended inter-frame space (EIFS) may be utilized to defer if aframe is detected but not correctly received. In the current 802.11,EIFS=aSIFSTime+ACKTxTime+DIFS. If the system utilizes a short ACK forall ACK transmissions, or if the STAs know that the short ACK is beingutilized, STAs may use a redefined EIFS or a newly defined EIFS_SACK todefer. For example, EIFS_SACK=aSIFSTime+SACKTxTime+DIFS, whereSACKTxTime is the time required to transmit an S-ACK frame at the lowestdata rate.

The originator may assign the ACK sequence ID for the short ACK frame inthe data packet. The ACK sequence ID may be implicitly indicated. Forexample, the ACK sequence ID may be determined as a function of one orany (full or partial) combination of the following parameters: ascrambler seed (6 bits), FCS (4 bytes), CRC in the SIG field (4 bits), alength field in the SIG field (9-21 bits), and/or a basic service setidentity (BSSID) (6 bytes).

Alternatively, the ACK sequence ID may be explicitly indicated. Forexample, the ACK sequence ID may be indicated by using a Service filedin the data frame. FIG. 4 shows an example PPDU data frame format. ThePPDU 400 includes a preamble 410, a SIG field 420, and a data field 430.The data field 430 includes a service field 432, an MPDU 434, and tailand padding bits 436. The service field 432 is a 16-bit field. The first7 bits of the service field 432 are the scrambler initialization bits,which are used to synchronize the descrambler and are set to zeronormally. The remaining 9 bits of the service field 432 are currentlyreserved. The reserved 9 bits of the service field 432 may be used toexplicitly assign the ACK sequence ID.

The originator may indicate in its data packet that a short ACK frame isexpected in response to the data packet. This indication may be providedby using the SIG field 420 (e.g., using 1 bit in the SIG field 420 toindicate that a short ACK frame is expected or acceptable) or theservice field 432 (e.g., using 1 bit (e.g., Bit 7) in the service field432 to indicate that a short ACK frame is expected or acceptable).

In another embodiment, the recipient may respond to the data frame witha short ACK frame and a short ACK indication may be included eitherexplicitly or implicitly in the short ACK frame. The AP and STAs(intended and unintended) may identify the frame as a short ACK framebased on the short ACK indication. Due to the simple structure of theshort ACK frame, receiving STAs may determine that it is a short ACKframe before starting the correlation detection of the ACK sequence.

The short ACK indication may be included in the STF field. The STFincludes several repetitions of a sequence. For example, most of the802.11 systems contain 10 repetitions of the STF sequence, while the802.11ah STF for 1 MHz has 20 repetitions. In one embodiment, the signof one or more repetition of the STF sequence may be flipped to indicatethat the frame is a short ACK frame. FIG. 5 shows a normal PPDU 510 andan example short ACK frame 520 with a short ACK indication. In FIG. 5,the sign of the last two STF sequences 522 is flipped to indicate thatthe frame is a short ACK frame. This will change the autocorrelationbehavior, so that the receiver may detect that this is a short ACKframe.

In another embodiment, an extended number of repetitions of the STFsequence may be used to indicate a short ACK frame. FIG. 6 shows anormal PPDU 610 and an example short ACK frame 620 with an extended STF622. Once the receiver detects a longer than normal STF orautocorrelation platform, it may determine that the frame is a short ACKframe.

An ACK frame is modulated and coded in the physical layer beforetransmission. The modulation and coding scheme (MCS) may be the highestrate in the BSSBasicRateSet parameter that is less than or equal to therate (MCS) of the previously received data frame. In this way, the STAsin the BSS have the capability to detect the ACK frames.

In order to reduce the overhead from ACK, a higher MCS may be morepromising since it may require less number of OFDM symbols to transmit.In some 802.11 standards, an ACK indication field is defined in the SIGfield and transmitted by the originator. ACK indication is used toindicate the information about the following ACK frame. For example, in802.11ah, ACK indication has the following definitions (00: ACK; 01: BA;10: No ACK; 11: a frame that is not ACK, BA or CTS). With ACKindication, unintended STAs may figure out whether the following frameis an ACK frame. Thus, it is not necessary that the STAs have tounderstand the ACK frame body. In one embodiment, the requirement ofchoosing an MCS for an ACK frame in the BSSBasicRateSet may be relaxedwhen an ACK indication is employed in the SIG field. Without ACKindication transmitted in the SIG field from the originator, theunintended STAs have to decode the ACK frame to figure out that this isan ACK frame. Thus, the ACK frame should use a basic MCS which can beunderstood by all the STAs. It has to be an MCS defined inBSSBasicRateSet. With ACK indication in the SIG field from theoriginator, the unintended STAs may detect the SIG field and notice thatan ACK frame is coming, and defer for a certain duration. In this way,the other STAs do not need to decode the ACK frame at all, so the ACKframe may use any MCS other than that defined in BSSBasicRateSet.

In another embodiment, the originator may assign an MCS and/or bandwidthfor the ACK frame, and the recipient may transmit an ACK frame with apre-assigned MCS and/or bandwidth.

In 802.11ah, receivers should support both 1 MHz and 2 MHz reception,while 1 MHz is required to be supported at the transmitter side.Therefore, it is possible that an AP transmits a 2 MHz packet to a STAand indicates explicitly or implicitly in the data packet that thefollowing ACK will be transmitted with 1 MHz. Alternatively, a STA maytransmits a 1 MHz packet to the AP and the AP, which is operating on a 2MHz channel, has a choice to reply with either 1 MHz or 2 MHz ACK.Transmitting the ACK with 2 MHz may reduce the ACK overhead. In theabove example, the STA may indicate the bandwidth utilized by the AP forACK transmission.

In another example, a STA may have two receive radio frequency (RF)chains but one transmit RF chain. Once the STA transmits one data streampacket to an AP, with current standards, the AP may transmit ACK withone data stream. However, if the channel condition is very good,allowing the AP to transmit the ACK with two data streams may be moreefficient. In one embodiment, the STA may check the channel conditionwhen it receives the previous two data stream packet from the AP, anddetermine if it is suitable for the AP to transmit the ACK with two datastreams.

When an originator transmits a data packet to a recipient, if theoriginator has some knowledge of the channel from the recipient to theoriginator and is aware of the asymmetrical transmit and receivecapabilities, the originator may determine a specific MCS and/orbandwidth for the ACK frame and indicate it in the data frame.Otherwise, the originator may choose an MCS equal to or lower than theMCS used in the previous data packet and choose bandwidth according tothe capabilities of the originator and the recipient.

The selected MCS and bandwidth for the following ACK frame may beindicated in the MAC header of the data packet. FIG. 7 shows aconventional MAC frame format. In the current 802.11 standards, an ACKpolicy subfield is defined in a QoS control field 710 of the MAC header.The ACK policy subfield is 2 bits in length and identifies theacknowledgment policy that is followed upon delivery of the MPDU. In oneembodiment, the ACK policy subfield may be extended for MCS andbandwidth indication. The number of bits needed for MCS and bandwidthinformation may vary depending on the standards. For example, with802.11ah, 2 bits may be used to indicate the bandwidth as shown in Table1.

TABLE 1 [B0, B1] Meaning 00 1 MHz 01 2 MHz 10 Same bandwidth as previouspacket 11 Reserved

Alternatively, the MCS and bandwidth for the ACK frame may be explicitlyindicated in the SIG field. For example, several bits may be added inthe SIG field to represent the MCS and bandwidth for the ACK frame.

Alternatively, the MCS and bandwidth for the ACK frame may be implicitlyindicated by setting a Duration field 720 in the MAC header. A Durationfield 720 in the MAC header may be set to the time value required totransmit the pending packet plus one ACK or block ACK plus shortinter-frame space (SIFS) interval. The duration value of the ACK orblock ACK may be calculated with the pre-assigned MCS and bandwidth.

When an ACK frame is transmitted with a pre-assigned MCS and bandwidth,the NAV setting may be modified accordingly. The Duration field 720 ofthe MAC frame transmitted by the originator holds a time value whichindicates the duration the originator expects the medium to be busy.Conventionally, the originator does not assign an MCS to the followingACK frame. Therefore, the originator estimates the duration of thefollowing ACK transmission based on the lowest MCS supported by thesystem. With the pre-assigned MCS in accordance with the embodimentsdisclosed herein, the originator may estimate the following ACKtransmission with the assigned MCS, and give a more accurate time valuein the Duration field 720. In this way, unintended STAs may set the NAVmore accurately.

Once the recipient correctly demodulates the data packet, it prepares anACK packet accordingly. When explicit indication is utilized, therecipient may transmit the ACK frame with the pre-assigned MCS andbandwidth. When implicit indication is utilized, the recipient maytransmit the ACK frame with an MCS and bandwidth which may complete theACK transmission within the specified duration. The MCS and bandwidthutilized by the recipient may not be required to be identical to thatchosen by the originator. However, the ACK PPDU duration may need to fitinto the duration value set by the originator in the MAC header.

The ACKs or BAs for a plurality of users (e.g., STAs) may be transmittedvia a single ACK or BA transmission. The ACKs (or BAs) for a pluralityof users may be aggregated in a spatial domain and transmitted usingmulti-user multiple-input multiple-output (MU-MIMO) or aggregated in atime domain and transmitted using an aggregated multi-user ACK.

In one embodiment, the MU-MIMO PPDU format may be used to transmit adelayed multi-user ACKs or block ACKs. FIG. 8 shows an example of PPDUframe structure for a MU-MIMO block ACK. The PPDU includes an omniportion 810 and a MU portion 820. The omni portion 810 is transmittedfor all users and the MU portion 820 is transmitted via each spatialstream of the MU-MIMO transmission. The omni portion 810 includes anSTF, an LTS and a SIG field (SIGA). The MU portion 820 includes an STF,LTFs, and an ACK body frame 822. The ACK body frame 822 shown in FIG. 8is a BA frame 830. Alternatively, the ACK body frame 822 may be a normalACK frame. The multi-user block ACK may be applied to a delayedmulti-user block ACK.

FIG. 9 shows an example message exchange sequence for delayed MU-MIMOblock ACK. STA1 acquires a channel and negotiates with an AP with a fewmessage exchanges 910 to set up a block ACK session with the AP withdelayed block ACK policy. An originator (STA1 in this example) transmitsdata, followed by a block ACK request (BAR) 914. The BAR frame 914solicits an ACK frame 916 from the recipient (AP in this example). FIG.10 shows a BAR frame format. The BAR frame 914 includes a BAR controlfield 1002. If a BAR ACK policy field in the BAR control field 1002 isset to ‘1’, the recipient returns an ACK immediately upon receipt of theBAR frame 914. If a BAR ACK policy field in the BAR control field 1002is set to ‘0’, the recipient does not send an ACK upon receipt of theBAR frame 914. In the example shown in FIG. 9, the AP sends an ACK 916in response to the BAR frame 914. During each BA session, unintendedSTAs (all STAs other than the originator (STA2-STA4 in this example) andthe recipient (AP in this example)) may set their NAV during the BAsession. The AP will hold the BA for STA1, and wait for delayedtransmission.

STA2 then acquires a channel and exchanges messages 920 to set up a BAsession with the AP and transmits data frames 922 and a BAR frame 924 tothe AP, and receive an ACK frame 926 from the AP. STA3 then acquires achannel and exchanges messages 930 to set up a BA session with the APand transmits data frames 932 and a BAR frame 934 to the AP, and receivean ACK frame 936 from the AP. STA4 then acquires a channel and exchangesmessages 940 to set up a BA session with the AP and transmits dataframes 942 and a BAR frame 944 to the AP, and receive an ACK frame 946from the AP.

The AP may group several block ACKs (BA1-BA4 in this example) andtransmit them using a MU-MIMO transmission, (i.e., delayed MU-MIMO BA).The AP may group multiple block ACKs according to some groupingcriteria, (e.g., with similar access category (AC), or good spatialchannel correlation), for MU-MIMO block ACK transmission.

The AP may modulate the BAs with different MU-MIMO weights, andtransmits them simultaneously. Within the MU-MIMO BA frame, the BA ACKpolicy field in the BA control field indicates whether an ACK isrequested in response to the BA frame. The BA ACK policy field may beset to ‘0’ or ‘1’ for all users. If the BA ACK policy field is set to‘1’, the BA frame 950 will not solicit an ACK response from theoriginator (STA1-STA4 in this example). If the BA ACK policy field isset to ‘0’, the BA frame 950 solicits an ACK response 960 from theoriginators (STA1-STA4 in this example) as shown in FIG. 9.

The ACK responses 960 from the STAs in response to the MU-MIMO BA 950may be transmitted by the STAs simultaneously using MU-MIMO.Alternatively, the STAs may transmit an ACK sequentially, for example,according to the user position array defined in a group ID. The group IDmay be included in the SIG field.

All AP/STAs involved in the delayed MU-MIMO ACK sequence may declare thesupport of delayed block ACK and MU-MIMO.

In another embodiment, instead of transmitting ACKs or BAs for multipleusers with MU-MIMO, the ACKs or BAs may be aggregated in time domain andtransmitted sequentially, (i.e., an aggregated multi-user ACK(A-MU-ACK)). A receiver (STA or AP) receives data packets, and generatesacknowledgement packets in response to received data packets, and mayaggregate the acknowledgement packets and transmit the aggregatedacknowledgement packets in the single transmission.

FIG. 11 shows an example PPDU structure for an A-MU-ACK frame. In FIG.11, the ACKs are aggregated at the MPDU level. The aggregated ACKs maybe block ACKs or normal ACKs. The PPDU for the A-MU-ACK 1100 includes apreamble 1110, an SIG field 1120, and a data field 1130. Within the datafield 1130, the A-MU-ACK frame 1132 is included. The A-MU-ACK frame 1132includes ACK (or BA) MPDUs 1142 for one or more users (ACK1, ACK2, ACK3in this example) separated by ACK delimiters 1144. The ACK/BA MPDUs 1142are aggregated at a MAC level and the A-MU-ACK frame 1132 is passed tothe physical layer as an aggregated MPDU packet so that the A-MU-ACKframe 1132 may be coded and modulated by the physical layer as a wholepacket. The lowest MCS may be used for the A-MU-ACK.

An ACK delimiter 1144 may be inserted at the beginning of each ACK/BAMPDUs 1142. The ACK delimiter 1144 may be 32 bits or 8 bits in length. A32-bit ACK delimiter may include a length field, a CRC and an 8-bitsignature field. The length field may be used to indicate the length ofthe following ACK/BA MPDU. The signature field may be used to detect anACK delimiter when scanning for a delimiter. An 8-bit ACK delimiter mayinclude an 8-bit signature field, which is used to detect an ACKdelimiter when scanning for a delimiter.

The aggregated multi-user ACK packet may be broadcast or multicast tomore than one user (e.g., STA). Since different users may have differentradio link quality due to path-loss, channel condition, receiversensitivity, etc., using the same MCS for all users in the sameaggregated multi-user ACK packet may be simple but may not be efficient.In addition, if a relatively lower MCS is chosen, all the users may notdecode the aggregated multi-user ACK frame correctly.

The ACK or BA MPDUs aggregated into the multi-user ACK frame may becoded with a separate MCS, as shown in FIGS. 12 and 13. In the examplesshown in FIGS. 12 and 13, three ACK/BA MPDUs included in an aggregatedmulti-user ACK frame are separately encoded with three MCSs (that may ormay not be the same). The length and MCS for each MPDU may be indicatedin the SIG field. In FIG. 12 the aggregated multi-user ACK frameincludes a common SIG field 1220 for three ACK MPDUs 1210 a-1210 c. InFIG. 13, a separate SIG field 1320 a-1320 c is included for each ACK/BAMPDU 1310 a-1310 c.

Multi-user aggregation may be performed after constellation mapping andbefore inverse discrete Fourier transform (IDFT). In this way, for allof the coded ACK frames other than the last frame, one padding and tailbit field may be added. There is no need to insert more padding bits toround up to an integer number of OFDM symbols. For the last coded ACKframe, both tail and padding bits may be inserted if necessary. Thelength field in the SIG field may indicate explicitly the length of eachACK body frame in bytes with this scheme.

Alternatively, multi-user aggregation may be performed after IDFT,(i.e., the aggregation is in the unit of OFDM symbols). Each coded ACKframe may occupy an integral number of OFDM symbols. Therefore, thetails bits and the OFDM symbol padding bits may be added for each codedACK frame. The length field in the SIG field may indicate the length ofeach ACK body frame in the unit of bytes or OFDM symbols.

FIG. 12 shows an example of aggregated multi-user ACK with a common SIGfield 1220. FIG. 13 shows an example of aggregated multi-user ACK withseparate SIG fields 1320. In both FIGS. 12 and 13, each ACK/BA MPDU maybe encoded with a separate MCS.

In the examples shown in FIGS. 12 and 13, all the users may use thecommon preamble 1230, 1330 for channel estimation. Therefore, the use ofMIMO schemes may be limited. For example, if space time block coding(STBC) scheme is utilized, the STBC may be utilized for all users in thepacket and different MIMO schemes may not be used for some of the users.

In another embodiment, various MIMO schemes may be utilized intransmission of the aggregated multi-user ACK frame, for example, usingthe PPDU structure shown in FIG. 14. FIG. 14 shows an example ofaggregated multi-user ACK with a separate LTF for each user forimplementing various MIMO schemes for the users. In FIG. 14, a dedicatedLTF 1402, (LTF1, LTF2, LTF3 in this example) is included for each userfor AGC adjustment and channel estimation. The length of the dedicatedLTF for each user may depend on the number of data streams transmittedand whether AGC is needed. With separate LTFs, different MIMO schemesmay be used for different users (in this example, beamforming for user 1and user 3, and STBC for user 2).

In another embodiment, a hierarchical modulation may be used tosimultaneously transmit ACKs for different users within differentconstellations of the same OFDM symbol(s). Hierarchical modulation canmultiplex multiple data streams, (e.g., for different users), into onesingle symbol stream, where base-layer symbols and enhancement-layersymbols are synchronously overplayed before transmission.

The acknowledgement may be piggybacked in a data packet, (i.e.,piggyback ACK). With a piggyback ACK, a data frame is overloaded with anacknowledgment of a previously received MAC protocol data unit (MPDU)and/or a poll to the STA to which the frame is directed. A piggybackedACK is used to reduce the overhead required for feedback ofacknowledgements.

The ACK and the data to which the ACK is piggybacked may be directed toa single user, (i.e., single user piggyback ACK). FIG. 15 shows anexample of single user piggyback ACK. An originator transmits a datapacket 1510 to a recipient. If the data is not time sensitive, apiggyback ACK may be used. The originator may indicate (e.g., in thedata packet) that a piggyback ACK is allowed. If the recipient has datapayload 1530 directed to the originator, the recipient may piggyback theACK 1520 with the data packet 1530. The piggyback ACK may be immediateor delayed. If the recipient has no data payload to the originator, therecipient may delay the ACK, (i.e., piggyback the ACK with data later).

The single user piggyback ACK may be performed in an MSDU level. FIG. 16shows an example of single user piggyback ACK aggregated in an MSDUlevel. An ACK (or BA) MSDU 1610 and a data MSDU 1620 are aggregated, anda modified MAC header 1630 may be added to the aggregated ACK and dataMSDUs. The MAC header 1630 may indicate that the subtype of the frame isa data frame with a piggybacked ACK or BA. Once the subtype field in theframe control field in the MAC header indicates the frame is a dataframe with a piggybacked ACK or BA, the sequence control field in theMAC header may be extended to cover the sequence number of the data MSDUand ACK. If a BA is utilized, the BA control field may be included inthe MAC header.

Single user piggyback ACK may be performed in the MPDU level. FIG. 17shows an example of piggyback ACK in an MPDU level. An ACK MPDU 1710 anda data MPDU 1720 are aggregated, and passed to the physical layer. Acommon PLCP header and preamble are added to the aggregated packet toform a PPDU 1700. In this scheme, an ACK MPDU 1710 and a data MPDU 1720may be coded and modulated with the same MCS. The ACK and data areincluded into separate MPDUs with a separate MAC header and the MPDUsare separated by MPDU delimiters.

Single user piggyback ACK may be performed in the PPDU level. FIG. 18shows an example of piggyback ACK in a PPDU level. ACK and data areincluded in separate MPDUs, and the MPDUs are modulated and codedseparately. A separate MCS may be used for the MPDUs. As shown in FIG.18, a common SIG field may be utilized in which MCS for ACK and data aredefined. Alternatively, separate SIG fields may be included.

The single user piggyback packet may include more than one data packetand/or more than one ACK/BA packet.

The ACK and data may be directed to different users, (i.e., multi-userpiggyback ACK). The piggyback ACK may be immediate or delayed. FIG. 19shows an example of multi user piggyback ACK. An originator transmits adata packet 1910 to a recipient. If the data is not time sensitive, theoriginator may allow a piggyback ACK. In this case, the originator mayindicate (e.g., in the data packet) that a piggyback ACK is allowed. Therecipient may choose to piggyback the ACK 1920 with a data packet 1930directed to a third STA.

Multi user piggyback ACK may be performed in an MPDU level. In thiscase, ACK and data MPDUs are aggregated, and passed to a physical layer.A MAC header of each MPDU packet has its own receiver address (RA)information. A common PLCP header and preamble are added to theaggregated packet to form a PPDU. In this scheme, ACK and data MPDUs maybe coded and modulated with the same MCS. Similar to the single userpiggyback ACK, multi user piggyback in the MPDU domain may utilize theframe format shown in FIG. 17.

Multi user piggyback ACK may be performed in a PPDU domain. In thiscase, ACK and data are in separate MPDUs, and may be modulated and codedseparately. A common SIG may be used in which an MCS for ACK and dataare defined. Alternatively, separate SIGs may be used.

Multi user piggyback ACK packets may include more than one data packetand/or more than one ACK or BA packet.

Embodiments for delayed multi-user ACK (DMA) setting up are explainedhereafter. DMA may be an efficient ACK mechanism that can effectivelyreduce the overhead for data packets by acknowledging packets frommultiple users simultaneously.

A STA may indicate to an AP during association or any other time thatthe STA is capable of receiving delayed multi-user ACKs. In order tofacilitate the delayed multi-user ACKs, three new action frames, AddDelayed Multi-user ACK Request Action frame (ADDDMA Request), AddDelayed Multi-user ACK Response Action frame (ADDDMA Response), andDelete Delayed Multi-user ACK frame (DELDMA) may be defined.

The ADDDMA frame is used to set up or to modify delayed multi-user ACKfor a specific traffic class (TC) or traffic stream (TS). The ADDDMAResponse frame is sent in response to an ADDDMA Request frame. TheDELDMA frame is sent by either the originator or the recipient toterminate the delayed multi-user ACK participation.

The three new action frames may, for example, be implemented using theconventional block ACK action frame. Example block ACK action fieldvalues for the ADDDMA Request, ADDDMA Response, and DELDMA frames areshown in Table 2.

TABLE 2 Block ACK Action field value Meaning 3 ADDDMA Request 4 ADDDMAResponse 5 DELDMA 6 DMA Request 7 DMA 8-255 Reserved

An ADDBA Request frame may be used as a format of the ADDDMA Requestframe. FIG. 20 shows a conventional ADDBA Request frame action fieldformat. The Block ACK action field 2002 may be set to ‘3’ to indicatethat this is an ADDDMA Request frame. The Block Ack Policy bit in theBlock Ack Parameter Set 2004 may be interpreted as, if set to “0”,regular delayed multi-user ACK for the STA, not for a specific trafficclass (TC) or traffic stream (TS), and, if set to “1”, delayedmulti-user ACK for the STA for a specific TC or TS specified by thetraffic identifier (TID) field in the Block Ack Parameter Set 2004.Several bits in the Block Ack Timeout Value field 2006 or in otherfields may be used to indicate the delayed multi-user ACK options:scheduled delayed multi-user ACK, unsolicited delayed multi-user ACK, orsolicited delayed multi-user ACK.

An ADDBA Response frame may be used as a format of the ADDDMA Responseframe. FIG. 21 shows a conventional ADDBA Response frame action fieldformat. The Block Ack Action field 2102 may be set to ‘4’ to indicatethat this is an ADDDMA Response frame. The Block Ack Policy bit in theBlock Ack Parameter Set 2104 may be interpreted as, if set to “0”,regular delayed multi-user ACK for the STA, not for a specific TC or TS,and if set to “1”, delayed multi-user ACK for the STA for a specific TCor TS specified by the TID field in the Block Ack Parameter Set 2104.Several bits in the Block Ack Timeout Value field 2106 or in otherfields may be used to indicate the delayed multi-user ACK options:scheduled delayed multi-user ACK, unsolicited delayed multi-user ACK, orsolicited delayed multi-user ACK.

A DELBA frame may be used as a format of the DELDMA frame. FIG. 22 showsa conventional DELBA frame. The Block Ack Action field 2202 may be setto ‘5’ to indicate that this is a DELDMA frame. One of the reserved bitsof the DELBA Parameter Set field 2204 (bit 0-10) may be interpreted as,if set to “0”, delete the delayed multi-user ACK for the STA, not for aspecific TC or TS, and if set to “1”, delete the delayed multi-user ACKfor the STA for a specific TC or TS specified by the TID field in theDELBA Parameter Set 2204.

A STA may indicate to a receiving STA or AP, that it is capable of andwilling to use the delayed multi-user ACK mechanism by sending an ADDDMARequest frame to the receiving STA/AP. The STA may indicate to areceiving STA/AP that it is initiating the delayed multi-user ACK forjust one TS or TC originated from itself by sending an ADDDMA Requestframe and set the Block Ack Policy bit to “1” and the TID field to theTID of the TS or TC.

The receiving STA/AP may respond by sending an ADDDMA Response frame.The receiving STA/AP, after receiving the packets from the STA and otherSTAs with which it has set up a delayed multi-user ACK may record thepackets received. The receiving STA/AP may later send a delayedmulti-user ACK frame at a pre-set time in case of scheduled delayedmulti-user ACK or unsolicited delayed multi-user ACK or at the requestof one of more STAs in case of solicited delayed multi-user ACK.

The transmitting and receiving STAs or AP may delete the delayedmulti-user ACK arrangement by transmitting a DELDMA frame, which may beimmediately acknowledged by the other party in the delayed multi-userACK.

After a STA transmits its packet, the packet may not be immediatelyacknowledged by the receiving STA/AP, since the receiving STA/AP mayaccumulate packets from more STAs and then acknowledge themsimultaneously using a delayed multi-user ACK frame.

Since STAs may be battery powered, it may be desirable to have STAstransmit their packets, go to a doze state, and wake up at apre-determined time to receive a delayed multi-user ACK frame from therecipient (e.g., AP). In case of scheduled delayed multi-user ACK, theoriginator (e.g., STA), which has already set up DMA arrangement withthe recipient, may go to a doze state immediately after their owntransmission, and may wake up at the delayed multi-user ACK transmissioninterval following their own transmissions to receive a delayedmulti-user ACK frame from the recipient. The recipient may indicate thedelayed multi-user ACK transmission intervals in a beacon, or a shortbeacon or other types of management, control, or action frame.

If the originator discovers that its packets are not received by therecipient successfully by evaluating the delayed multi-user ACK frame,the originator may immediately retransmit the packets that are notpositively acknowledged or may retransmit at a later point of time.

In case of unsolicited delayed multi-user ACK, the recipient, (e.g.,AP), may decide that it has received enough number of packets fromoriginators (e.g., STAs) that have already set up DMA arrangement withthe recipient, and may transmit a delayed multi-user ACK frame toacknowledge all packets received.

In case of solicited delayed multi-user ACK, originators (e.g.,transmitting STAs), which have already set up DMA arrangement with therecipient, may transmit a DMA Request frame to the recipient at somepre-determined or random intervals. The recipient may then transmit adelayed multi-user ACK frame to acknowledge all packets received afterreceiving one or more DMA Request frames soliciting a delayed multi-userACK frame.

The DMA Request frame may be implemented, for example, by using a blockACK action frame or any other management or control frame. The Block AckAction field value may be set to ‘6’ to indicate that this is a DMARequest frame if implemented as a block ACK action frame. The DMARequest frame may include a DMA Request option field to indicate whetherthe DMA request is for an entire group or for an individual STA, and/ora DMA option field to indicate whether the DMA request is for justregular ACK or for block ACK.

STAs may be pre-arranged into groups either autonomously or by an AP.For example, an AP may announce STA group memberships using a group IDmanagement frame or any other management or control frames. The receiveraddress in the MAC header of the delayed multi-user ACK frame for agroup of STAs may be either a broadcast or multicast MAC address that ismutually agreed by the STAs and the AP.

The delayed multi-user ACK frame for pre-arranged groups of STAs may beimplemented using a block ACK action frame or any management or controlframe. The block ACK action field value may be set to ‘7’ to indicatethat this is a delayed multi-user ACK frame for a pre-arranged group ofSTAs if implemented as block ACK action frame.

The delayed multi-user ACK frame for a pre-arranged group of STAs mayinclude an ACK option field to indicate that the DMA is for apre-arranged group of STAs and indicate whether the ACK is either anormal ACK or a block ACK. The delayed multi-user ACK frame for apre-arranged group of STAs may also include a block ACK option field toindicate whether the block ACK for each member of the pre-arranged groupis multi-TID (Multi TID), whether the block ACK for each member of thepre-arranged group is multi TID and the number K of TIDs per STA beingacknowledged (Number of TIDs per STA), and/or the number N of framesthat are being acknowledged per TID per member of the pre-arranged group(Number of ACKed frames per TID).

The delayed multi-user ACK frame for a pre-arranged group of STAs mayinclude a field indicating the number of ACK fields. The delayedmulti-user ACK frame for a pre-arranged group of STAs includes ACKfields. FIG. 23 shows an example of ACK fields in the delayed multi-userACK frame for a pre-arranged group of STAs. The ACK fields may bearranged in the same order as the order of the STAs in the pre-arrangedgroup. Each ACK field may comprise K (TID+TID ACK) fields. The number Kis specified by Number of TIDs per STA in the block ACK option field.The TID ACK field may include a starting sequence number and a bit mapof N bits each indicating an ACK for a frame for the associated TID.

A delayed multi-user ACK frame for an ad-hoc group of STAs may beimplemented using a block ACK frame or any management or control frame.The delayed multi-user ACK frame for an ad-hoc group of STAs may includeidentification, which is a field that indicates this is a DMA frame. Theblock ACK action field value may be set to 7 if implemented as block ACKAction frame.

The delayed multi-user ACK frame for an ad-hoc group of STAs may includea DA field. The destination address in the MAC header in the DMA may bea multicast or a broadcast address mutually agreed by the STAs and theAP. The delayed multi-user ACK frame for an ad-hoc group of STAs mayinclude an ACK Option field. The ACK Option field may indicate that theDMA is for ad hoc group, and may indicate whether the ACK is either anormal ACK or a block ACK.

The delayed multi-user ACK frame for an ad-hoc group of STAs may includea block ACK Options to indicate whether the block ACK for each member ofthe ad hoc group is multi TID (Multi TID), whether the block ACK foreach member of the ad hoc group is multi TID and the number K of TIDsper STA being acknowledged (Number of TIDs per STA), and the number N offrames that are being acknowledged per TID per member of the ad hocgroup (Number of ACKed frames per TID).

The delayed multi-user ACK frame for an ad-hoc group of STAs may includea field (Number of ACK fields) to indicate the number of ACK fieldscontained in the current DMA frame. The delayed multi-user ACK frame foran ad-hoc group of STAs includes an ACK field. FIG. 24 shows an exampleof ACK fields in the delayed multi-user ACK frame for ad hoc group ofSTAs. Each ACK field is for each member of the ad hoc group. Each ACKfield starts with an ID field, which contains the ID of the member ofthe ad hoc group. The ID may be MAC address, association ID (AID) orother form of IDs that the STAs and the AP agreed upon. Each ACK fieldincludes K (TID+TID ACK) fields. The number K is specified by Number ofTIDs per STA in Block ACK option field. The TID ACK field may include astarting sequence number and a bit map of N bits each indicating an ACKfor a frame for the associated TID.

A short ACK frame is a shortened version of an ACK frame, which has noMAC layer fields. A short BA frame is a shortened version of a BA frame,which has no MAC layer fields. FIG. 25 shows a conventional short ACKframe format. The conventional short ACK frame includes an STF field2502, an LTF field 2504, and an SIG field 2506. The SIG field 2506 ofthe short ACK frame has an indication that the frame is a short ACKframe and other indications and signaling such as ACK ID to indicate theintended receiver of the short ACK, a More Data field, and a Durationfield for NAV setting. The short BA frame has the same structure as theshort ACK frame. The short BA frame includes an STF field, an LTF field,and an SIG field. The SIG field of the short BA frame has an indicationthat the frame is a short BA frame and other indications and signalingneeded for the short BA frame such as Block Ack ID to indicate theintended receiver of the BA, starting sequence control and block bitmap.

The 802.11ah standard provides a mechanism for an early ACK indication.The SIG field includes ACK indication bits (2 bits) to indicate the typeof acknowledgment expected as a response to the frame to beacknowledged. The ACK indication bits are set “00” for ACK, “01” for BA,and “10” for no ACK, and “11” is currently reserved.

If a STA skips decoding a packet after PHY preamble to save power or isnot able to decode the rest of the packet correctly, the STA may not beable to obtain the Duration value from the MAC header to update its NAVfor medium access purposes. In such a case, the STA may defer mediumaccess by the duration of EIFS or EIFS-DIFS+AIFS [AC] after detection ofthe medium being idle. DIFS is DCF inter frame space and AIFS isarbitration inter frame space (used by the QoS facility for a givenaccess category). EIFS is defined as EIFS=SIFS+DIFS+ACK Time where ACKTime is the time required to transmit an ACK frame at the lowestphysical layer supported rate.

In one embodiment, an originator (STA or AP) may request or indicatethat a short ACK or a short BA (either the conventional format or theformat shown in FIG. 2 in accordance with one embodiment disclosedabove) may be sent in response to the frame by a recipient (AP or STA)instead of a regular ACK or BA. When a short ACK or short BA is usedinstead of a regular ACK or regular BA, respectively, the MAC protocolsmay be enhanced to provide increased efficiency. FIG. 26 shows anexample of short ACK response. The originator sends a data frame 2602 toa recipient along with a short ACK indication in the data frame 2602,and the recipient sends a short ACK 2604 in response. The short ACKindication may be extended to a short BA indication. The originator maysend a block ACK request (BAR) or an aggregated MPDU (AMPDU) with animmediate BAR along with a short BA indication, and the recipient maysend a short BA in response.

The originator may convey the short ACK indication or short BAindication (hereinafter collectively “short ACK indication”) by usingthe “10” value of the ACK indication bits in the SIG field. The ACKindication value of “10” is also used to convey “No ACK” response. Thesetwo indications may be combined in the “10” value of the ACK indicationas follows. A “Short EIFS” may be specified for these two cases in placeof the EIFS. For these two cases an unintended STA that does not havethe Duration value from the MAC header to update its NAV may defermedium access by the duration of the Short EIFS after detection of themedium being idle. The Short EIFS may be defined as ShortEIFS=SIFS+DIFS+Short ACK Time where Short ACK Time is the time requiredto transmit a Short ACK frame. The Short ACK Time may be defined as theaddition of the time lengths of its fields (for example time lengths ofSTF, LTF, and SIG fields added together for 1 MHz or 2 MHz and higherbandwidth modes as the case may be). Alternatively, the Short ACK Timemay be calculated as the time required for transmitting the Short ACKframe content at the lowest PHY supported rate. The short EIFS may alsobe defined as Short EIFS=SIFS+DIFS+Short BA Time where Short BA Time isthe time required to transmit a short BA frame.

Alternatively, the originator of a frame may convey the short ACKindication in any part of the physical layer portion of the frame (e.g.,in the preamble using one or more bits or a subfield in the SIG field).

Alternatively, the originator may convey the short ACK indication in aMAC portion of the frame, (e.g., in the MAC header). For example, theshort ACK indication may be indicated in a control field of a MAC headeror by reusing any of the existing fields or bits in the MAC header.

A device (STA or AP) that receives a frame directed to it with anindication that a short ACK or a short BA needs to be sent in responsemay respond with a short ACK frame or a short BA frame, respectively.The short ACK frame or short BA frame may be sent after an SIFS ofreceiving the frame with the short ACK or short BA indication.

The STA and the AP may indicate their capabilities and preferences ofusing short ACK or short BA to acknowledge packets, for example, duringthe association process using existing or new IE, field, subfield in theassociation request and association response frames.

Alternatively, a short ACK or a short BA may be the acknowledgementresponse that is allowed (i.e., short ACK or short BA may be usedinstead of the normal ACK or normal BA frame).

When a normal ACK or normal BA is used, the value in the Duration fieldof a frame is typically estimated by the transmitter using the lowestMCS supported by the system. This tends to overestimate the Duration andtherefore leads to medium usage inefficiency since the duration field isused by unintended STAs in the system to set the NAV for medium access.When a short ACK or short BA is to be used, the transmitter (STA or AP)may set the duration value in the Duration field of the MAC header moreaccurately by using the time required to transmit the short ACK frame orthe short BA frame. This will result in a more accurate Duration valueand therefore leads to medium usage efficiency since the duration fieldis used by unintended STA receivers in the system to set their NAV formedium access.

The short ACK or short BA mechanism may be applied to the aggregatedtransmissions. An AMPDU is an aggregated MAC PDUs. A regular ACK frameor regular BA frame may be transmitted in an AMPDU. A short ACK or shortBA may not be transmitted by a STA or an AP as part of an AMPDU. A shortACK or a short BA may be transmitted by a STA or an AP as part of anaggregated PPDU where several physical layer packets are aggregated toincrease medium usage efficiency in reduced inter frame space (RIFS)burst where more than one packet is transmitted in succession with anRIFS spacing between the packets. The RIFS is a smaller than the SIFS.

A short CTS frame is a shortened version of a CTS frame, which has noMAC layer fields. The short CTS frame includes an STF field, an LTSfield, and an SIG field. The SIG field of the short CTS frame includesan indication that the frame is a short CTS frame and other indicationsand signaling such as a CTS ID to indicate the intended receiver of theCTS frame, bandwidth, and Duration for NAV setting.

A transmitter (STA or AP) of a request-to-send (RTS) frame (i.e.,initiator) may request or indicate that a short CTS frame should be sentin response to the RTS frame by the intended receiver (AP or STA) of theRTS frame (i.e., responder).

In one embodiment, such short CTS indication may be conveyed within anRTS frame by reusing the “10” value of the ACK indication bits in theSIG field. The ACK indication bits of “10” are also used to convey “NoACK” response. These two indications or cases may be combined in the“10” value of the ACK indication bits as follows. A “Short EIFS” may bespecified for these two cases in place of the EIFS. For these two cases,an unintended STA that does not have the Duration value from the MACheader to update its NAV may defer medium access by the duration ofShort EIFS after detection of the medium being idle. The Short EIFS isdefined as Short EIFS=SIFS+DIFS+Short CTS Time. The Short CTS Time maybe defined as the addition of the time lengths of its fields (i.e., timelengths of STF, LTF, and SIG fields added together for 1 MHz and 2 MHzand higher bandwidth modes). Alternatively, the Short CTS Time may becalculated as the time required for transmitting the Short CTS framecontent at the lowest physical layer supported rate. The Short ACK Timemay be the same as a Short CTS Time and the Short ACK Time may be usedin place of the Short CTS Time because the short ACK frame and the shortCTS frame have the same format and length even though some of thecontent they carry is different.

Alternatively, the transmitter of an RTS frame (i.e., initiator) of aframe may convey the short CTS indication in any part of the physicallayer portion of the frame (e.g., in the preamble using one or more bitsor a subfield in the SIG field).

Alternatively, the transmitter of an RTS frame (i.e., initiator) mayconvey the short CTS indication in a MAC portion of the frame, (e.g., inthe MAC header). For example, the short CTS indication may be indicatedin a control field of a MAC header or by reusing any of the existingfields or bits in the MAC header.

A device (STA or AP) that receives an RTS frame directed to it with anindication that a short CTS needs to be sent in response may respondwith a short CTS frame. The short CTS frame may be sent after an SIFS ofreceiving the RTS frame with the short CTS indication.

The STA and the AP may indicate their capabilities and/or preferences ofusing a short CTS frame to respond to an RTS frame, for example duringthe association process using any existing or new IE, field, subfield inthe association request and association response frames.

Alternatively, a short CTS may be the response allowed for an RTS frame(i.e., a short CTS is used instead of the regular CTS frame).

When an RTS frame is sent by a device (AP or STA), the device may setthe NAV for devices in its neighborhood. However, a response CTS may notbe received by the neighbor devices. For example, the intended receiver(STA/AP) of the RTS frame may fail to respond with a CTS frame or theremay be a failure in the reception of the CTS frame. According to the802.11 standards, a STA that made its last NAV update based on thereception of an RTS frame may reset its NAV after a CTS timeout intervalstarting from the end of the reception of the RTS frame if no receptionis detected during the CTS timeout interval. The CTS timeout interval iscalculated as (2×SIFS)+(CTS Time)+Receiver Start Delay+(2×Slot Time)where SIFS and Slot Time are system parameters. The CTS Time iscalculated using the length of the CTS frame and the data rate at whichthe RTS frame was received.

In one embodiment, when a device (STA or AP) transmitting an RTS frameindicates that its response frame is a short CTS frame or if a short CTSframe is the response allowed for an RTS frame, a Short CTS Timeoutinterval may be used instead of the CTS Timeout interval. For example,the short CTS Timeout interval may be obtained as (2×SIFS)+(short CTSTime)+Receiver Start Delay+(2×Slot Time) where SIFS and Slot Time aresystem parameters. The Short CTS Time may be defined as the addition ofthe time lengths of its fields (e.g., time lengths of STF, LTF, and SIGfields added together). Alternatively, the Short CTS Time may becalculated as the time required for transmitting the short CTS framecontent at the lowest physical layer supported rate.

When a device (STA or AP) transmitting an RTS frame indicates that itsresponse frame should be a short CTS frame or if a short CTS frame isthe response allowed for an RTS frame, a Short CTS Time as describedabove may be used in estimating the time to set in the Duration/ID fieldof the RTS frame.

The 802.11ah standard has introduced a speed frame exchange protocolwhich is enabled by the use of a More Data field and a Response Framefield. The More Data field is a 1 bit field that indicates whether ornot there is more data to be sent. The More Data field allows theresponding STA to set the Response Frame field appropriately. TheResponse Frame field (or ACK indication bits) is a 2 bit fieldindicating the type of a following frame. The Response Frame field maybe set to “00” for ACK, “01” for BA, “10 for No ACK, and “11” for aframe that is not ACK, CTS, or BA (i.e., it indicates that the responseframe is a data frame).

FIGS. 27 and 28 show example procedures of a speed frame exchange fordownlink and uplink data, respectively. In FIG. 27, a STA sends aPS-Poll frame 2702 to an AP to retrieve data. The AP responds with anACK 2704 with a More Data field set to ‘1’ and a Response Frame fieldset to “11.” The AP then sends a data frame 2706 with a More Data fieldset to ‘0’ and a Response Frame set to “00.” The STA receives the dataframe 2706 and sends an ACK frame 2708 with a More Data field set to ‘0’and a Response Frame field set to “10.”

In FIG. 28, a STA sends a data frame 2802 to an AP with a More Datafield set to ‘1’ and a Response Frame field set to “00.” The AP thensends an ACK frame 2804 with a More Data field set to ‘0’ and a ResponseFrame field set to “11.” The STA then sends another data frame 2806 witha More Data field set to “0’ and a Response Frame field set to “00.” TheAP then sends an ACK frame 2808 with a More Data field set to ‘0’ and aResponse Frame field set to “10.”

In one embodiment, a short ACK frame and a short BA frame may be used inspeed frame exchanges. A short ACK may be used in response to thePS-Poll frame or the data frame. A short BA frame may be used inresponse to an AMPDU. The SIG field of the short ACK frame and the shortBA frame may include a Response Frame field (or ACK indication field)and/or a More Data field. The Response Frame field (or ACK indicationfield) may be used in conjunction with the More Data field of the shortACK frame or the short BA frame to conduct speed frame exchange.

FIG. 29 shows an example of speed frame exchange using a short ACK frame(or short BA frame) for downlink data. A STA sends a PS-Poll frame 2902to retrieve data from an AP. The AP responds with a short ACK frame 2904with a More Data field set to ‘1’ and a Response Frame field set to“11.” The AP sends a data frame 2906 (or an AMPDU) with a More Datafield se to ‘0’ and a Response Frame field set to “short ACK” fornon-aggregated data frame or “short BA” for aggregated data frame. TheSTA then responds with a short ACK (or a short BA) 2908 depending on thereceived data type with a More Data field set to ‘0’ and a ResponseFrame field set to “10.”

FIG. 30 shows an example of speed frame exchange using a short ACK (orshort BA) frame for uplink data. A STA sends a data frame 3002 (or anAMPDU) to an AP with a More Data field set to ‘1’ and a Response Framefield set to “short ACK” or “short BA” depending on the data type. TheAP then sends a short ACK frame 3004 (or a short BA) with a More Datafield set to ‘0’ and a Response Frame field set to “11.” The STA thensends another data frame 3006 (or AMPDU) with a More Data field set to“0’ and a Response Frame field set to “short ACK” or “short BA.” The APthen sends a short ACK frame 3008 (or short BA) with a More Data fieldset to ‘0’ and a Response Frame field set to “10.”

As an example, the Response Frame field (or ACK indication field) valuemay be set to “00” to indicate short ACK and “01” to indicate short BA,or alternatively, set to “10” to indicate short ACK and short BA.

In another embodiment, a short PS-Poll frame may be used in speed frameexchanges. The SIG field of the short PS-Poll frame may include one orboth of a Response Frame field (or ACK indication field) or a More Datafield. The short PS-Poll from the STA indicates that the response is ashort ACK frame and also that there is more data to be transmitted.

FIG. 31 shows an example of speed frame exchange using a short PS-Pollframe and a short ACK (or short BA) frame. A STA sends a short PS-Pollframe 3102 to retrieve data from an AP with a More Data field set to ‘1’and a Response Frame field set to “short ACK.” The AP responds with ashort ACK frame 3104 with a More Data field set to ‘0’ and a ResponseFrame field set to “11.” The STA sends a data frame 3106 (or an AMPDU)with a More Data field se to ‘0’ and a Response Frame field set to“short ACK” for non-aggregated data frame or “short BA” for aggregateddata frame. The AP then responds with a short ACK 3108 (or a short BA)depending on the received data type with a More Data field set to ‘0’and a Response Frame field set to “10.”

The More Data field may be set based on whether the STA has uplink dataor not. If the short PS-Poll frame is sent by the STA in an unscheduledwakeup event, then the Response Frame field may be set to indicate shortACK because the AP will most likely send an acknowledgement rather thandata.

In regular MAC frames, the Duration field in the MAC header is used forsetting the NAV for unintended receivers of the frame. However shortframes (e.g., short ACK, short BA, short CTS) may not have the Durationfield and may not carry the duration information.

In case where a STA wakes up from a sleep state and monitors the mediumto receive a frame sequence to set its NAV, the STA may continue toperform clear channel assessment (CCA) until a regular frame (not ashort frame) is detected with a Duration field, a short frame withduration information is detected, or the elapse of a period of timeequal to the ProbeDelay that is a specified as a system parameter. If ashort frame is received and if it contains a duration field orinformation in the SIG field, the STA may use it to set its NAV. If ashort frame is received and if it does not contain a duration field orinformation, the STA may ignore the frame for NAV setting purposes.

In case where an unintended STA receives a short frame and the shortframe does not include a duration field or information, the unintendedSTA may not update its NAV but retain its existing NAV setting. Theexisting NAV setting may have been triggered by the duration setting inthe earlier frames of the frame exchange sequence (e.g., sounding framesequence in case of a short beamforming report (BR)-Poll, data and ACKframe sequence in case of a short BA).

If the short frame has a duration field or information, the unintendedSTA may update its NAV based on the duration field or information if thenew NAV value is greater than the current/existing NAV value.

In case an unintended STA receives a short PS-Poll frame, the unintendedSTA may update its NAV settings using duration required to transmit theresponse frame (e.g., data, ACK, short ACK) plus one SIFS interval, ifthe new NAV value is greater than the current NAV value. Alternatively,the unintended STA may update its NAV setting using a default responseframe or response frame duration specified in the system if the responseframe is not indicated in the short PS-Poll frame. Alternatively, theunintended STA may update its NAV setting using duration required totransmit the response frame (e.g., data, ACK, short ACK) indicated inthe short PS-Poll frame plus one SIFS interval, if the new NAV value isgreater than the current NAV value. The unintended STA may include inthe duration calculation any required overhead frame or additionalresponse frame (e.g., ACK frame) to the response frame indicated in theshort PS-Poll frame and associated SIFS interval.

In one embodiment, the short frames (e.g., short BA, short BR-Poll, andshort Probe Request) may include a Duration field or information in theSIG field for NAV setting. The size of the SIG field may be increased,for example, by using a higher MCS.

When a STA initiates communication with the AP using an initiating ortrigger frame (e.g., PS-Poll frame or data frame), the STA may establishits transmission opportunity (TXOP) duration by setting the Durationfield of its frame and thereby setting the NAV of unintendedreceivers/STAs. In speed frame exchange when there is downlink datatransmitted by the AP and the STA is the TXOP holder or TXOP initiator,the STA may estimate the duration for the entire TXOP (entire sequenceof multiple frames) initially and use that to set the duration field inthe frame it transmits to set the NAV. For example, the estimate may bebased on one or more of any data to transmit, expected data to bereceived, expected MCS to be used, and inter-frame spaces (e.g., SIFS).The STA may truncate any excess unused TXOP duration with a CF-Endframe.

Alternatively, the STA may estimate the duration for its initiating ortrigger frame, any required response frame(s), overhead frames andinter-frame space(s) (e.g., SIFS) and set the Duration field in itsinitiating/trigger frame based on the estimate. The STA may then extendthe TXOP duration every time the AP indicates that there is more data(More Data field=1). The STA may not extend the TXOP duration beyond thespecified TXOP duration limit for the given QoS transmission (e.g.,specified by EDCA rules).

The STA may truncate a medium reservation or TXOP duration for speedframe exchange using a CF-End frame when there is no data to send orreceive.

The AP sets the duration value in the frames it transmits based on theduration value in the frames it receives from the STA.

In case where an unintended STA receives a PS-Poll frame, the unintendedSTA may update its NAV setting using a duration required to transmit theresponse frame (e.g., data, ACK, short ACK) plus one SIFS interval, ifthe new NAV value is greater than the current NAV value. Alternatively,the unintended STA may set its NAV setting using a default responseframe or response frame duration specified in the system if the responseframe is not indicated in the PS-Poll frame. Alternatively, theunintended STA may set its NAV setting using a duration required totransmit the response frame (e.g., data, ACK, short ACK) indicated inthe PS-Poll frame plus one SIFS interval, if the new NAV value isgreater than the current NAV value. The unintended STA may include inthe duration calculation any required overhead frame or additionalresponse frame (e.g., ACK frame) to the response frame indicated in thePS-Poll frame and associated SIFS interval.

A station sends a probe request frame when it needs to obtaininformation from another station. Instead of a regular probe requestframe, a short probe request frame may be used. The short probe requestframe includes an STF field, an LTF field, and an SIG field. The SIGfield of the short probe request frame includes an indication that theframe is a short probe request frame amongst other indications andsignaling needed such as access network option, partial SSID andindication of whether probe response or short beacon is expected as aresponse to the short probe request frame.

When a STA receives a short beacon with a change sequence that isdifferent from the STA's stored change sequence the STA may need toupdate its system information. The system information update may be doneusing a probe request frame carrying the change sequence to trigger theAP to send an optimized probe response frame including systeminformation elements that need to be updated by the STA and the changesequence.

Since it is smaller in size, using an NDP probe request frame is moreefficient than using a regular probe request frame which would occupymore medium time especially when there are a large number of STAswanting to update system information. Power consumption at the STAs isalso reduced by using the NDP probe request frame. This is especiallyuseful when a full beacon is not transmitted frequently or a shortbeacon is used in the BSS.

In one embodiment, the NDP probe request frame may include the changesequence stored in the STA. This may be done, for example, by using asmall size change sequence (e.g., a 4 bit sequence rather than an 8 bitsequence) that can be accommodated within the limited bits available inthe SIG field.

The NDP probe request frame may indicate what system informationelements are needed by the STA (e.g., a bit map representing the subsetof system information elements). The NDP probe request frame mayindicate that the change sequence in the last received short beacon isdifferent than the change sequence stored in the STA.

The NDP probe request frame may indicate which set of predefined systeminformation elements are needed by the STA. The sets of predefinedsystem information elements may be indexed and the index representing aset of system information may be signaled in the NDP probe requestframe. For example, a predefined set of system information elements maybe a set of system information elements or fields containing mandatoryinformation such as timestamp, beacon interval, and capability; a set ofsystem information elements or fields containing other information suchas EDCA parameters, Quiet element, BSS load, channel switchannouncement, HT operation element, VHT operation element; or a set ofsystem information elements or fields containing any combination ofmandatory information and other information. For example, the abovesignaling may be implemented by using one or more bits of the reservedbits in the SIG field of the NDP probe request frame.

When a STA sends an NDP probe request frame including the changesequence stored in the STA, the AP may send an optimized probe responseframe including system information elements that need to be updated bythe STA and the change sequence. The AP is able to do this by storingthe previous change sequences and the corresponding changed systeminformation element's IDs. The AP finds the updated information to sendby comparing the received change sequence from the STA with its storedprevious change sequences.

When a STA sends an NDP probe request frame indicating what systeminformation elements are needed, the AP may send an optimized proberesponse frame including system information elements that need to beupdated by the STA and the change sequence.

When a STA sends an NDP probe request frame indicating which set ofpredefined system information elements are needed, the AP may send anoptimized probe response frame including the indicated set of predefinedsystem information elements and the change sequence.

When a STA sends an NDP probe request frame indicating that the changesequence in the last received short beacon is different than the changesequence stored in the STA, the AP may send an optimized probe responseframe including a predefined or basic set of system information elementsthat need to be updated by the STA and the change sequence.

In any embodiments above, the response to the NDP probe request framemay be a short probe response frame that includes the informationrequested or indicated in the NDP probe request frame.

An NDP PS-Poll frame may be used for active polling. The NDP PS-Pollframe includes an STF field, an LTF field, and an SIG field. The SIGfield of the short PS-Poll frame has an indication that the frame is ashort PS-Poll frame and other indications or signaling needed for theshort PS-Poll frame such as AID or partial AID of the transmitting STA,BSSID or partial BSSID of the BSS in which the STA is associated, andpreferred MCS for the STA to receive data from the AP.

The NDP PS-Poll frame may include signaling to request a BSS changesequence and/or current timestamp. The signaling may be included in theSIG field of the NDP PS-Poll frame. One or more bits of the SIG fieldmay be used to indicate a change sequence request and/or a currenttimestamp request from the AP. One or more bits of the SIG field may beused to indicate whether one or more of the following fields areincluded: preferred MCS, a change sequence request, and a currenttimestamp request.

When a STA sends an NDP PS-Poll frame containing a request for BSSchange sequence, the AP may send the BSS change sequence immediately ina response frame or indicate in the response frame to the STA that itshould check the beacons. When a STA sends an NDP PS-Poll framecontaining a request for the current timestamp, the AP may send thecurrent timestamp immediately in a response frame or indicate in theresponse frame to the STA that it should check the beacons.

Any of the frames from the AP that are transmitted in response to thePS-Poll frame such as ACK or data may carry the requested informationfrom the AP. Alternatively, a new response frame from the AP may bedefined for the PS-Poll frame to carry the requested information fromthe AP. This frame may be of any type such as management, control, ordata.

Although the embodiments are described herein with respect to IEEE802.11 protocols, it should be understood that the embodiments areapplicable to any wireless communication systems. Although SIFS is usedas an inter-frame spacing in various embodiments, all other inter framespacing such as RIFS or other agreed time interval may also be used.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

1. A method for use in a station of transmitting acknowledgements inresponse to data packets in wireless communication, the methodcomprising: receiving data packets from a plurality of stations;generating acknowledgements for the data packets; obtaining atransmission opportunity; and transmitting the acknowledgements for thedata packets to the plurality of stations in a single transmission. 2.The method of claim 1 wherein the acknowledgements are transmitted usingmulti-user multiple-input multiple-output (MU-MIMO).
 3. The method ofclaim 2 wherein the acknowledgements are transmitted after apredetermined time from receiving the data packets.
 4. The method ofclaim 3 wherein the acknowledgements are transmitted based on an agreedschedule or a solicitation by one of the plurality of stations, or on acondition that a predetermined number of data packets are received. 5.The method of claim 1 wherein generating acknowledgements for the datapackets includes generating acknowledgement packets, and aggregating theacknowledgement packets, and wherein transmitting the acknowledgementsincludes transmitting the aggregated acknowledgement packets to theplurality of stations in the single transmission.
 6. The method of claim5 wherein the acknowledgement packets are aggregated in a medium accesscontrol (MAC) service data unit, in a MAC protocol data unit (PDU), orin a physical layer convergence protocol (PLCP) protocol data unit(PPDU).
 7. A method for use in a station of transmitting anacknowledgement in wireless communication, the method comprising:receiving a frame that indicates a sequence identity (ID); andtransmitting a short acknowledgement (ACK) frame in response to thereceived frame, wherein the short ACK frame includes an ACK sequencecorresponding to the sequence ID.
 8. The method of claim 7 wherein theshort ACK frame includes a short training field (STF) and the ACKsequence.
 9. The method of claim 7 wherein the short ACK frame istransmitted with a short ACK indication.
 10. The method of claim 7wherein the short ACK frame is transmitted in response to an indicationincluded in the frame.
 11. A wireless transmit/receive unit (WTRU) fortransmitting acknowledgements in response to data packets in wirelesscommunication, the WTRU comprising: a processor configured to receivedata packets from a plurality of stations, generate acknowledgements forthe data packets, and transmit the acknowledgements for the data packetsto the plurality of stations in a single transmission.
 12. The WTRU ofclaim 11 wherein the processor is configured to transmit theacknowledgements using multi-user multiple-input multiple-output(MU-MIMO).
 13. The WTRU of claim 12 wherein the processor is configuredto transmit the acknowledgements after a predetermined time fromreceiving the data packets.
 14. The WTRU of claim 13 wherein theprocessor is configured to transmit the acknowledgements based on anagreed schedule or a solicitation by one of the plurality of stations,or on a condition that a predetermined number of data packets arereceived.
 15. The WTRU of claim 11 wherein the processor is configuredto generate acknowledgement packets, aggregate the acknowledgementpackets, and transmit the aggregated acknowledgement packets in thesingle transmission.
 16. The WTRU of claim 15 wherein the processor isconfigured to aggregate the acknowledgement packets in a medium accesscontrol (MAC) service data unit, in a MAC protocol data unit, or in aphysical layer convergence protocol (PLCP) protocol data unit (PPDU).17. A wireless transmit/receive unit (WTRU) for transmitting anacknowledgement in wireless communication, the WTRU comprising: aprocessor configured to receive a frame, and transmit a shortacknowledgement (ACK) frame in response to the received frame, whereinthe received frame indicates a sequence identity (ID) and the short ACKframe includes an ACK sequence corresponding to the sequence ID.
 18. TheWTRU of claim 17 wherein the short ACK frame includes a short trainingfield (STF) and the ACK sequence.
 19. The WTRU of claim 17 wherein theshort ACK frame is transmitted with a short ACK indication.
 20. The WTRUof claim 17 wherein the short ACK frame is transmitted in response to anindication included in the frame.